The Ins and the Outs on Part Number 16797 PWM Controller. Historically, cooling fans run at 100%, even when less airflow is needed, constantly turning on and off as the engine temperature changes. This REACTION-based temperature control system causes constant amperage spikes, excessive noise and premature wear. The Derale PWM fan controller continuously monitors your engine’s temperature, therefore CONTROLLING the temperature and increasing the vehicles cooling efficiency, while reducing the amps used to do so. Here’s how it works. The controller monitors your engine temperature via the side of the radiator, therefore providing a more accurate reading for your cooling system. Using Soft Start Technology, fans ramp up slowly which eliminates harmful AMP spikes. Our new control will keep your fan/s running for an additional 20 seconds after you turn your vehicle off. The unit will continuously monitor your engine’s temperature and operate the fans at the optimum fan rate as needed between 1 to 100%. The net result the electric fans often only run between 40-60% to keep your engine cool. Additional benefits include reduced fan speeds which means reduced fan noise, which tends to compete with that sweet sound of your engine! This multi-fan controller has a built-in A/C Over-ride circuit and is designed to control as many 12 volt brushed electric fans as desired, up to 70 Amps combined. Operating range can be set from 130°F to 240°F. Even better, installation and calibration is a snap. It simply wires in-between your vehicle’s battery and electric fans.